RDMA/uverbs: Make the code in ib_uverbs_cmd_verbs() less confusing

This patch reduces the number of #ifdefs and also avoids that
smatch reports the following:

drivers/infiniband/core/uverbs_ioctl.c:276: ib_uverbs_cmd_verbs() warn: if statement not indented
drivers/infiniband/core/uverbs_ioctl.c:280: ib_uverbs_cmd_verbs() warn: possible memory leak of 'ctx'
drivers/infiniband/core/uverbs_ioctl.c:315: ib_uverbs_cmd_verbs() warn: if statement not indented

References: commit fac9658c ("IB/core: Add new ioctl interface")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Acked-by: Matan Barak <matanb@mellanox.com>
Cc: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>